In an office located nearly 2,000 feet above his island estate, Bill Lichtenstein is overseeing construction of the new headquarters for the public radio show "The Infinite Mind."

None of this actually exists in the real world, but rather in a 3-D virtual world known as Second Life. Here, "The Infinite Mind" is planning to broadcast its weekly one-hour radio program on health and science and create an immersive experience.

"This represents an unprecedented leap forward for broadcasting into virtual reality and 3-D online communities," said Lichtenstein, president of Lichtenstein Creative Media in Cambridge, which produces "The Infinite Mind." "There's a huge potential to bring people together in a dynamic, cost-effective environment."

Bill Lichtenstein of Lichtenstein Creative Media, Cambridge, in his office and as an avatar in the Second Life virtual world. In Second Life, people can choose to be their idealized selves.

When "The Infinite Mind" opens it virtual doors next month, it will become the first regularly scheduled national media broadcast within the increasingly popular 3-D web space. A growing number of companies are turning to these interactive worlds as a place to reach vast audiences in a new way. Next week, merchant American Apparel is hosting a grand opening party for its first virtual store in Second Life, where residents can buy clothes for their animated online personas, known as avatars, or purchase merchandise for their real-life selves.

Second Life, which opened to the public in 2003, has its own economy, upwards of 340,000 residents, and a virtual land mass now larger than Boston. It's accessible for free through secondlife.com and more than 60,000 residents are joining this virtual world every month, according to David Fleck , vice president of marketing for San Francisco's Linden Lab, which operates Second Life.

All the content in these virtual worlds is created by the residents, who can include anyone from American Apparel to your little brother. Currently, about 7 percent of Second Life is in stealth mode, invisible to the public while businesses, academics, and others like "The Infinite Mind" develop spaces to market their brands and create communities.

"Second Life goes outside of everything else. It's not a game, not the actual Internet," Fleck said. "So as eyeballs migrate away from traditional forms of media -- television, radio, print -- virtual worlds offer a new way for businesses to inject their brands. And the interactivity is almost unlimited."

For "The Infinite Mind," which airs in more than 250 public radio markets, the virtual headquarters will offer incredible access for visitors. The 16-acre campus features a broadcast studio with a glassed-in viewing gallery where virtual residents can attend live radio show tapings and ask questions during the interviews. The producers and guests will all appear as avatars in the same room. In the real world, the shows are taped in front of audiences only once a year; usually the host, producer, and guests are in different cities.

A 100-seat amphitheater will offer film screenings and musical performances, including one by Suzanne Vega, who next month will be the first major recording artist to perform live in Second Life avatar form.

At the virtual boutique, visitors can purchase "Infinite Mind" t-shirts for their customized avatar or their real selves.

And residents will also have a chance to make real donations via the virtual world. (Second Life users can convert real dollars into a virtual currency, which they can use to buy real and virtual products.)

Lichtenstein said he's partnered with the architects who designed his virtual headquarters -- coincidentally named Infinite Vision Media -- to develop similar virtual spaces for businesses, nonprofits, and other groups.

Second Life and other virtual communities like it present a major untapped opportunity to reach out to real people and their alter egos, according to Paul Hemp , senior editor of the Harvard Business Review, who published an article last month, "Avatar-Based Marketing."

Although some people create avatars that look and act like their real selves, many people use the chance to be what they always wanted to be or at least want to try for awhile. The average height of avatars in Second Life is 7 feet tall. Everyone seems thinner, and usually more attractive.

Some males choose to be females in Second Life, and vice versa.

"Clothing styles you might not normally try or afford might end being a real-world purchase if you like using them in the virtual world," Hemp said.

American Apparel web services director Raz Schionning said the company considered advertising in video games, but it's expensive to get in blockbuster titles, and if the game flops, marketers get dragged down with it. Virtual worlds, however, let companies push the boundaries in how they communicate with customers .

American Apparel's virtual store, modeled after its Tokyo shop, opened unofficially last month, and since then has sold 3,000 items to avatars.

At the grand opening next week, the merchant plans to release its new fall denim collection in Second Life -- months before it hits stores.

The company is also giving a 15 percent discount on real-life merchandise to anyone who buys virtual clothes for their avatar. (These are sold at a much lower cost -- about $1 per item).

"We want the store to be fun, sexy, and edgier than our other stores," said American Apparel spokeswoman Alexandra Spunt . "We're just trying to have some fun. There aren't the same rules."